Vehicle body composed of a unit construction body (monocoque body) is configured by using, as main skeletal components, long longitudinal members such as side sill, roof rail, front floor having floor tunnel part, and side member, which are disposed as aligned in the front-back direction of the vehicle body; and long widthwise members such as floor cross member and roof cross member, which are disposed as aligned in the widthwise direction of the vehicle body. The longitudinal member and the widthwise member are generally joined with each other through flanges formed at the longitudinal (axial) ends of the widthwise member, in order to ensure rigidity of the vehicle body and to bear the load.
The widthwise member is applied with load in the axial direction thereof induced by deformation of the cross-sectional shape of the longitudinal member, and also with torsional moment induced by displacement of the longitudinal member. The widthwise member is, therefore, required to suppress deformation possibly caused by the load applied in the axial direction, and to have a high torsional rigidity which affects driving stability of vehicles.
To minimize the amount of deformation of the widthwise member, it is necessary to effectively apply the axial load to the cross section of the widthwise member, and to optimize the cross-sectional shape and joining conditions of the widthwise member.
Also for the purpose of elevating the torsional rigidity of the widthwise member, it is again necessary to optimize the cross-sectional shape and joining conditions of the widthwise member, similarly as described above.
For the purpose of suppressing deformation of the widthwise member under axial load, it is preferable to ensure a large cross-sectional area of the widthwise member, and to join the widthwise members with the longitudinal member at points in the flange as close as possible to the cross-sectional profile. On the other hand, for the purpose of enhancing the torsional rigidity of the widthwise member, it is again preferable to ensure a large cross-sectional area of the widthwise member. However, in contrast to the above-described conditions for suppressing deformation, it is preferable to join the widthwise member with the longitudinal member, at points in the flange as apart as possible from the cross-sectional profile. In short, while ensuring a large cross-sectional area of the widthwise member, the geometry of flange of the widthwise member and the points of joining are necessarily optimized, taking suppression of deformation and improvement in the torsional rigidity of the widthwise member into consideration.
Now the flange, which is formed at the longitudinal end of the widthwise member and serves as a joint part between the widthwise member and the longitudinal member, is molded by press molding as a result of extensional deformation. Accordingly, all efforts of forming the flange along the ridge part of the widthwise member will inevitably result in concentration of the extensional deformation locally at the edge of the flange. As a consequence, in the process of press forming, the flange would sometimes rupture at the edge thereof, when intended to be long enough in width.
It has therefore been a conventional practice to provide a notch at around the ridge part of the widthwise member, rather than providing the flange. Alternatively, even if the flange is formed along the ridge part of the widthwise member, the flange has been minimized in width in a portion thereof corresponded to the center in the perimeter direction of the ridge part. As a consequence, the widthwise member has no joining point, typically by spot welding, in the flange thereof especially in a portion corresponded to the ridge part. This has been one of the causes of inhibiting suppression of deformation and improvement in torsional rigidity of the widthwise member.
A specific explanation will be given below, referring to the case where the longitudinal member is configured by the side sills and the tunnel part of a front floor panel, and the widthwise member is configured by the floor cross member. The floor of the vehicle body (simply referred to as “floor”, hereinafter) not only primarily takes part in ensuring necessary levels of torsional rigidity and flexural rigidity of the vehicle body during driving, but also takes part in transmission of impact load in case of car crash, and largely affects the weight of vehicle body. The floor is therefore required to satisfy contradictory requirements regarding high rigidity and light weight. A general structure employed by the floor is such as having the front floor panel; and a floor cross member which is joined to the top surface (the surface faced to the cabin) of the front floor panel, and connects the tunnel part which is formed so as to bulge at around the widthwise center of the front floor panel, and side sill inner panels which are spot-welded to both widthwise edges of the front floor panel. By spot-welding the floor cross member to the front floor panel, the tunnel part, and to the side sill inner panels, the floor structure will be improved in rigidity, and in load transmission performance under impact load.
In the conventional process of spot welding of the floor cross member respectively to the top surface of the front, floor panel, the outer surfaces of the side sill inner panels, and to the vertical wall surface of the tunnel, part of the front floor panel, it was general to use an outward flange formed, as a welding margin, at both longitudinal ends of the floor cross member.
The floor cross member is a structural component which takes part in improving the rigidity of vehicle body and in absorbing impact load in case of side impact. In recent years, from the viewpoints of weight, reduction and improvement in collision safety, a thinner and more strong high tensile strength steel, for example a high tensile strength steel (HTSS) having a tensile strength of 390 MPa or larger, is used as a material for the floor cross member.
The high tensile strength steel has, however, suffered from a low design freedom of the floor cross member, due to its poor formability.
More specifically, for the case where the floor cross member is composed of a high tensile strength steel of 390 MPa or higher, the flange, which is formed at the end of the floor cross member to be serve as the joint part with the side sill inner panels or with the tunnel part, will be affected by a severe stretch flanging at the edge of the curved part, and may rupture in the process of press forming due to poor formability of the floor cross member. The floor cross member has, therefore, had to be compensated for the shortage of the formability typically by provision of a notch, rather than provision of the flange, at around the ridge part, while resigning itself to degradation in the torsional rigidity and load transmission performance. The notch has, however, been concerned about degradation of various performances of the floor cross member, including collision characteristic regarding axial collapse, and torsional rigidity.
Regarding this sort of technology, Patent Literature 1 discloses a floor structure directed to suppress deformation of vehicle interior in case of collision, by providing a means for reducing impact deformation strength, such as a notch, at the end of the floor cross member.
Patent Literature 2 discloses a floor structure in which the floor cross member is connected to a side sill, by connecting the floor cross member to a side sill reinforcement.
Patent Literature 3 discloses a floor structure elevated in the rigidity by welding the floor cross member and the side sill, by spot-welding the upper part of a side sill inner panel and the flange of the floor cross member.
Patent Literature 4 discloses a floor structure in which the floor cross member and the side sill are connected, by folding the edge of the side sill inner panel to be connected to the floor cross member.